164 HYPOPHYSIS AND GONADOTROPHIC HORMONES 



DIVISIONS PARTS 



Lobes 



neural component- 



pars enninens 

 pars nervosa 



(•,•) adeno component- 

 ^^ (epit-heliGJ ) 



pars tuberalis 

 pars intermedia 

 pars anterior 



Fig. 3.1. Diagrams representing sagittal sections of a conventionalized mammalian hypo- 

 physis showing the divisions, components and parts. The adeno-eminence and adenostalk 

 together form the pars tuberalis. The adenolobe is almost completely divided by the hypo- 

 physeal cleft into an anterior lobe and an intermediate lobe. In many mammals the anterior 

 lobe is entirely composed of pars anterior tissue and the intermediate is entirely composed of 

 pars intermedia tissue as shown here. For further details refer to the text. 



Adeno-eminonce Neural eminence 

 Adenostalk Neural stalk 



Adenolobe Neural lobe 



It must be added here that the division 

 between eminence and stalk is in some spe- 

 cies indefinite and cannot always be made; 

 the stalk is variable in extent, and in some 

 species it does not exist as a junctional re- 

 gion between the other divisions. Clearly the 

 division into eminence and stalk is of de- 

 scriptive value only and has no functional 

 significance. 



In most mammals, and in most other ter- 

 restrial vertebrates with the exception of 

 birds, Rathke's pouch adheres to the neural 

 component during development. The cavity 

 of Rathke's pouch persists in the adult as a 



flattened cavity — the hypophyseal cleft (re- 

 sidual lumen) — which allows an easy sepa- 

 ration of the adenolobe into two parts (Fig. 

 3.2) . The portion of adenolobe which is ad- 

 herent to the neural lobe is the intermediate 

 lobe. The composite structure formed by the 

 adherent neural and intermediate lobes is 

 called the posterior lol)e. The remaining por- 

 tion of the adenolobe is the anterior lobe. 

 Hypophyseal hormones are commonly ex- 

 tracted from the separated anterior and pos- 

 terior lobes. The anterior lobe hormones are 

 somatotrophin, prolactin, corticotrophin, 

 thyrotrophin, follicle-stimulating hormone 

 (FSH), and luteinizing hormone (LH), and 

 are the products of the pars anterior tissue 

 which the anterior lobe contains. Posterior 

 lobe hormones are intermedin, which derives 



